1. Field of the Invention
The present invention relates to optical fiber and hardware for connectorizing an optical fiber end. More particularly, the present invention relates to a system and method for clocking and affixing one or more multi-core fibers within a connector ferrule using light curable epoxy.
2. Description of the Related Art
Optical network operators are continuing to look for ways to obtain increased density of optical fiber networks. One method for packaging higher numbers of light carrying paths in a small space is Multi Core Fiber (“MCF”). A MCF typically comprises a central core surrounded by several satellite cores in a radial pattern surrounding the central core. Each of the cores is potentially a light carrying path, and the MCF thus provides multiple parallel paths for optical signal transmission and/or reception in a single fiber.
A MCF is known in the existing art. See for example, U.S. Pat. Nos. 5,734,773 and 6,154,594 and U.S. Published Applications 2011/0229085, 2011/0229086 and 2011/0274398, each of which is herein incorporated by reference. In the background art of U.S. Published Application 2011/0274398, as depicted in FIGS. 1 and 2, a MCF 180 has a central core 181 and multiple satellite cores 182, e.g., six satellite cores 182-1, 182-2, 182-3, 182-4, 182-5 and 182-6, in a common cladding layer 184. The satellite cores 182 are positioned around the central core 181 symmetrically, at the vertices of a regular hexagon 183.
Each of the central and satellite cores 181 and 182 exhibits a same diameter. The central core 181 and each of the satellite cores 182 has a diameter of about 26 micrometers (um), depicted as distance A in FIG. 2. A center to center spacing relative to the adjacent satellite cores 182 is about 39 um, depicted as distance B in FIG. 2. Other dimensions and spacing, besides those shown in U.S. Published Application 2011/0274398, as depicted in FIGS. 1 and 2, are known in the background art. Also, more or fewer satellite cores 182 are known in the background art.
Each of the central and satellite cores 181 and 182 may carry a unique light signal, and each MCF 180 is affixed within a channel of a ferrule of a connector for communicating its unique signals of the central and satellite cores 181 and 182 to a device via a port, or to further cabling via an adapter. FIG. 3 depicts a typical connector 201 having a cylindrical ferrule 203 presenting an end of a single MCF 180 for mating to another connector, via an adapter, or for communicating with a port of a device. FIG. 4 depicts an MT-type ferrule 303 having first and second holes 305 and 307 for accepting alignment pins of a matting ferrule. Between the first and second holes 305 and 307, the MT-type ferrule 303 presents an array of twelve fiber ends of MCFs 180-1 through 180-12 for communicating to MCFs of the matting ferrule. The fiber ends are between v-grooves in the ferrule 303 and a plate 308 attached to the ferrule 303. An access window 309 opens to the MCFs 180-1 through 180-12 residing the v-grooves and can be used to flood epoxy into the v-grooves, as is conventional in the art. Although it is known in the prior art to attach the plate 308 to the ferrule 303, as shown in U.S. Pat. Nos. 6,550,980 and 8,529,138, both of which are herein incorporated by reference, it is most common in the prior art for the structure above the v-grooves (e.g., represented by the plate 308 in FIG. 4) to be an integral portion of the ferrule 303. For example, US Patent Application Publication 2004/0189321, which is herein incorporated by reference, shows a typical MT ferrule wherein the structure above the fibers is an integral part of the ferrule and the v-grooves are replaced by circular channels. Hereinafter, the term holders is broad enough to encompass all structures holding a fiber, such as circular channels and v-grooves, and the ferrule is not limited to ferrules formed of two pieces, but also includes ferrules formed of a single piece. For example, reference numeral 308 refers to either a plate residing above the holders, e.g., v-grooves or channels of the ferrule, or a portion of the ferrule 303 residing above the holders.
Although FIG. 3 shows an LC type connector 201 and FIG. 4 shows a MT ferrule 303, which could be used in a MPO/MTP type connector, other connector styles for presenting a single MCF or multiple MCFs in an ordered array are known in the existing arts, such as ST, SC and MT-RJ. Further the row of MCFs presented by the ferrule 303 may include more or fewer MCFs, such as eight or sixteen MCFs in one or two or more rows.
Traditional optical fiber has a single central core along its axis. Mating two connectors requires precision alignment of the central axial cores between terminated fiber optic connectors to provide acceptable loss performance characteristics. With MCF 180, there are multiple satellite cores 182-X in addition to the central core 181 that also require lateral and axial alignment. Each of the cores 181 and 182-X in an MCF 180 must be aligned with a corresponding core in another MCF or port to which it will be connected. The “clocking” or rotation angle of the end face of one MCF 180 relative to another MCF 180 must therefore also be taken into account when a connection is made. Specifically, it would be beneficial to control the angular position of individual MCFs in a connector, such as an LC, SC, ST, MTRJ, MTP or MPO connector, so that the cores of each MCF are aligned and properly clocked with respect to the cores of a fiber at a mating connector/port. Hereinafter, the term connector will also encompass a device port.
MPO, MTP and MTRJ array type connectors align a plurality of fibers ends on one connector's termination face with a corresponding plurality of fibers ends on another connector's termination face. In these array type connectors, fiber alignment is handled by mating a pair of precision alignment pins in one array type connector with corresponding holes in the other array type connector, such as holes 305 and 307 depicted in FIG. 4. When the pins are inserted into the holes, the central axis of each individual fiber end of one connector is aligned with the central axis of each individual fiber end of the other connector. However, the alignment pins and holes of these connectors do not control for the axial rotational position of each MCF in the array because the array type connectors were designed for single core fibers and this angular relationship is not critical when single core fibers are mated.
LC, SC and ST connectors align a single fiber end captured within a cylindrical ferrule 203 of a first connector to a single fiber end captured within in a cylindrical ferrule 203 of a second connector. Like the array type ferrule 303 of FIG. 4, the single fiber is bonded within the cylindrical ferrule 203 using epoxy. The cylindrical ferrule 203 of the first connector is aligned to the cylindrical ferrule 203 of the second connector using a sleeve with a circular inner surface to receive a cylindrical ferrule 203 at each end. Typically, the sleeve is captured within an adapter housing and serves to bring the first and second ferrules 203 into end-to-end abutting, axial alignment. However, the sleeve of the adapter and the cylindrical ferrules 203 also do not control for the axial rotation or “clocking” position of the fiber end held by the ferrule 203 because the single fiber type connectors were design for single core fibers and this angular relationship is not critical when single core fibers are used.